Corrected: Prime Medicine partners with Cimeio to create shielded stem cell therapies

Prime Medicine and Cimeio Therapeutics are partnering to develop gene-edited stem cell treatments for two kinds of bone marrow cancers and other potential genetic diseases, such as Gaucher syndrome and Hurler syndrome.

Financial terms were not disclosed. As part of the deal, Prime will be developing a gene editor for CD117, an antigen found on many kinds of cells, both healthy and cancerous. With the gene editor, Cimeio hopes to create stem cell transplants which can be paired with immunotherapies. Currently, patients have to receive very intense conditioning with chemoradiation to kill off the cells in their bone marrow before they can get a stem cell transplant.

Cimeio’s goal is to use immunotherapy to selectively kill diseased stem cells only, and then deliver healthy stem cells. But in order to make sure the healthy stem cells aren’t destroyed by the immunotherapy, Cimeio edits CD117 to effectively hide those cells.

The edit doesn’t impact the function of the CD117 receptor, as it’s needed for blood cells to mature. Cimeio’s hope is that by hiding the transplanted stem cells via gene editing, diseased cells can be more gradually depleted and patients won’t need to undergo very toxic conditioning.

Cimeio, which is based in Basel, Switzerland and Boston, was founded three years ago, but debuted from stealth last year with $50 million from Versant Ventures. A number of biotechs have attempted to develop safer stem cell transplants, but have faced safety issues — one leukemia patient died after receiving Magenta Therapeutics’ treatment. Versant’s previous attempt with Graphite Bio to make safer stem cell transplants for sickle cell disease ended after a serious event of low blood cell counts.

Previously, Cimeio had been using homology-directed repair (HDR) to edit its cells, but that method cuts out a part of the DNA entirely, creating double-stranded breaks where it edits. Prime editing, on the other hand, does not create double stranded breaks and can be used to make multiple edits without running the risk of the DNA recombining the wrong way.

Moving forward, Cimeio will be focused on developing a prime-edited therapy and will be shelving its HDR program, CEO Tom Fuchs told Endpoints News.

“We knew from the beginning that to really fulfill the potential for what we can do with this technology, we need to be able to multiplex, so to be able to do more than one edit, so that we could develop combination shielded cells, where you’re shielding more than one target,” Fuchs said. He noted that talks with Prime began about a year ago, and the partners have been working on the research collaboration for the past six months.

The technology is still in its early days — no person has ever been treated with a prime-edited therapy. Fuchs expects that it will take approximately a year’s time for the partners to develop a CD117 prime editor.

Keith Gottesdiener

Afterwards, the companies will get exclusive options to each other’s technologies for certain diseases. With the prime-edited stem cell therapy, Cimeio plans to tackle acute myeloid leukemia and myelodysplastic syndrome, a blood cancer that can progress into AML. Prime will also have the option to license the CD117-shielded cells for genetic diseases outside of sickle cell disease, as well as to develop in vivo-edited stem cell therapies.

“BD is an area we’re going to be very busy in 2023,” Prime Medicine CEO Keith Gottesdiener said in a previous interview with Endpoints, noting that the biotech was looking for places not only to partner some of its existing programs, but also for technologies that could be complementary to its editing platform.

This story was corrected to note that the Graphite Bio patient did not die, but experienced a serious adverse event.

therapeutics
cell therapy
immunotherapy
stem cells
gene editing
biotech